This invention relates to a method for the cationic polymerization of olefins using catalysts comprising a cation and a compatible non-coordinating anion. This invention farther relates to the use of complexes containing a compatible non-coordinating anion to initiate cationic polymerization.
The cationic polymerization of olefins is typically conducted in the presence of catalyst systems comprising a Lewis acid, a tertiary alkyl initiator molecule containing a halogen, ester, ether, acid or alcohol group and occasionally an electron donor molecule such as ethyl acetate. The exact combination of the components varies with each system. The tertiary alkyl initiators used in these systems are used for living and non-living carbocationic catalysts and are typically represented by the formula: 
wherein R1, R2, and R3 are a variety of alkyl or aromatic groups or combinations thereof, n is the number of initiator molecules and X is the functional group on which the Lewis acid affects a change to bring about the carbocationic initiating site. This group is typically a halogen, ester, ether, alcohol or acid group depending on the Lewis acid employed. One or two functional groups per initiator tend to lead to linear polymers while three or more tend to lead to star polymers.
Catalyst systems based on halogens and/or alkyl containing Lewis acids, such as boron trichloride and titanium tetrachloride, use various combinations of the above components and typically have similar process characteristics. For living polymerization systems, Lewis acid concentrations typically must exceed the concentration of initiator sites by 16 to 40 times in order to achieve 100 percent conversion in 30 minutes (based upon a degree of polymerization equal to 890) at xe2x88x9275 to xe2x88x9280xc2x0 C.
Additional living systems disclosed in U.S. Pat. Nos. 4,929,683 and 4,910,321 discloses Lewis acids in combination with organic acids, organic esters, or organic ethers to form cationic polymerization initiators that also create a complex counter anion which is disclosed to not assist or cause proton elimination.
In non-living polymerizations, high molecular weight polyisobutylenes are only prepared at low temperatures (xe2x88x9260 to xe2x88x92100xc2x0 C.) and at catalyst concentrations exceeding one catalyst molecule per initiator molecule. Frequently, these catalysts are restricted in their use to certain narrow temperature regions and concentration profiles. An improved catalyst could be used stoichiometrically rather than in excess to provide enough initiation sites over a wide range of temperatures without affecting its suitability.
In another catalyst area, a new class of catalysts utilizing compatible non-coordinating anions in combination with cyclopentadienyl transition metal compounds (also called metallocenes) has recently been disclosed. Descriptions of these catalysts appear in EP-A-0 277 003, EP-A-0 277 004 and U.S. Pat. No. 5,198,401 and WO-A-92/00333. These disclose a preferred method of preparation wherein metallocenes (biscyclopentadienyl and monocyclopentadienyl transition metal compounds) are protonated by an anionic precursor such that an alkyl/hydride group is abstracted from a transition metal to make it both cationic and charge-balanced by the non-coordinating anion.
The use of ionizing compounds not containing an active proton is also known. See, EP-A-0 426 637 and EP-A- 0 573 403. An additional method of making ionic catalysts is disclosed in EP-A-0 520 732. Ionic catalysts for addition polymerization can also be prepared by oxidation of the metal centers of transition metal compounds by anionic pre-cursors containing metallic oxidizing groups along with the anion groups, see EP-A-0 495 375.
Methods of supporting ionic catalysts comprising metallocene cations and non-coordinating anions are described in WO 91/09882, WO 94/03506 and in co-pending U.S. Ser. No. 08/248,284, filed Aug. 3 1994 now abandoned. U.S. Pat. No. 5,066,741 discloses the preparation of syndiotactic polystyrene or poly(vinyl aromatics) using non-coordinating anions in combination with cyclopentadienyl transition metal derivatives under coordination catalysis conditions. (U.S. Pat. Nos. 5,196,490 and 4,808,680 disclose a similar preparation using an alumoxane.) These catalyst systems are employed at 70xc2x0 C. and are used both in non-polar solvents and in bulk.
Jordan, in the Journal of the American Chemical Society (1986, 108, 1718-1719) discloses that tetraphenyl boron forms stable complexes with bis cyclopentadienyl zirconium dimethyl, unhindered Lewis bases such as 4,4xe2x80x2-dimethyl-bipyridine and 4-(dimethylamino) pyridine in CH3CN and also disclosed that tetraphenyl boron is stable in THF solution.
In another area, the manufacture of a triisopropyl silylium has been reported in CandEN Nov. 8, 1993 and in Science, 262,402, 1993.
It is desirable that a new catalyst system utilizing compatible non-coordinating anions in polar or non-polar solvent be produced that can polymerize olefins heretofore only polymerizable by cationic catalyst as well as typical monomers polymerized by coordination catalysis, preferably at nearly the same time.
This invention relates in part to the discovery that a non-coordinating anion with certain cations form cationic polymerization catalyst systems. In addition this invention further relates to the discovery that monomer and/or temperature and/or solvent choice can determine the reaction mechanism (coordination versus cationic) for catalyst systems comprising a cyclopentadienyl transition metal derivative and a compatible non-coordinating anion.
Therefore, in accordance with this invention, there is provided a cationic polymerization catalyst system, a method for cationic polymerization using a catalyst system which comprises a compatible non-coordinating anion. Another aspect of the invention is directed toward certain novel catalyst systems for cationic polymerization and a method of using this catalyst system for the polymerization of cationically polymerizable olefins. A particularly desirable aspect is the polymerization by both coordination mechanism and cationic mechanism in the same reactor at about the same time.